1. Field of Invention
This invention relates to helicoptor rotor lead-lag dampers and more particularly to such dampers which are hydraulic devices of the piston and cylinder configuration which incorporate an external seal between their relatively moving parts so as to retain the fluid. This invention is addressed to improving the life of the seal by increasing its capability to resist wear. More particularly the invention relates to means for reducing the adverse effects of scuffing, bunching, or scraping, which is induced either axially or torsionally by a lack of anti-friction lubricant during motion of the device. Means are provided by this invention to both limit the torsion motion of the seal and also to provide a supplemental source of fluid to the external side of the seal.
2. Description of the Prior Art
Rotation prevention means have been used on hydraulic operating apparatus having telescopic shafts, wherein the object of the means is to preserve orientation of the shaft members. An example of such means is a telephone lineman's or fire truck extensible boom having a platform or bucket on its outer end. U.S. Pat. No. 2,666,417 to Harsch shows such apparatus having an internal non-circular guide preventing relative rotational motion of the telescopic shafts. There is no indication or suggestion in this prior art that the use of such a guide could provide an advantage to a seal. The motions and function of the boom apparatus are infrequent and not of an oscillatory or reciprocal nature. The stroke is long and slow, averaging only a few cycles per day, while in the damper field of this invention the strokes of a piston may average over 300 cycles per minute, with replacement times desired to be in excess of several thousand hours.
The effects of heat generated by this action, altitude of the aircraft involved, the influence of centrifugal force, material and weight restrictions all impose constraints on seal design not found in the environment of the Harsch patent.
Likewise, U.S. Pat. No. 2,244,150 to Greve illustrates the use of a guide between cooperating cylinders of a shock absorbing landing gear strut for the similar purpose of maintaining proper orientation of a wheel. This is also not an environment wherein extensive concern need be expressed for overworking of the dynamic seal.
The prior art includes various systems for the supplying of internal replacement hydraulic fluid to components, including helicoptor dampers such as shown in U.S. Pat. No. 2,604,953 to Campbell and to propeller hub bearings as shown in Pat. No. 2,160,745 to Levy. It is also known that damper seals may occasionally be designed so as to leak slightly in order to provide operation on a wetted surface for wear reduction purposes. The feature not apparent from this prior art, in addition to the teaching of the benefits of non-rotation, is the supplying of fluid to the outside or low pressure side of the dynamic seal so as to provide it with a wetted surface on which to operate without intentionally producing leakage. The prior art also includes U.S. Pat. No. 2,334,115 to Meredith, which teaches a dashpot configured to collect fluid leaking past the dynamic seal and return it to the inner pressure chambers. There is no teaching in this reference of the use of centrifugal force, nor is there an anti-rotation means included.